[BUG]: Sanity checks during schema creation

### What version of `drizzle-orm` are you using?

0.21.1

### Describe the Bug

Common mistakes like two columns with the same names, should be caught early, during schema creation:

```
const users = pgTable('users', {
id: serial('id').primaryKey(),
fullName: text('id'), // id field created twice
});
```

This can happen pretty easily while copy-pasting lines of code.